(a) Field of the Invention
The present invention relates to a valve system including a cam and a variable tappet.
(b) Description of the Related Art
Recently, cylinder de-activation (CDA) is being widely used in vehicle engines. CDA improves fuel efficiency by stopping function of some of a vehicle's cylinders in idle or low load driving conditions.
A traditional variable tappet CDA valve system includes a variable tappet provided on an upper end of a valve stem. The variable tappet includes an inner tappet, an outer tappet, and a locking pin. First cams corresponding to the outer tappet, and a shorter, second cam corresponding to the inner tappet, are provided on a camshaft. The inner and outer tappets may move together or separately, depending on the position of the locking pin (which is operated by hydraulic pressure). The stem can be moved either by the first cams or by the shorter second cam.
However, the variable tappets are provided to all valves, so production cost is high. Particularly, two tappets are disposed in each of intake/exhaust ports per cylinder, and sixteen variable tappets are needed for a double over-head cam (DOHC) four cylinder engine.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.